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A Guide to the Night Sky: September 2016


A Guide to the Night Sky
September 2016 

By Tre Gibbs, LAAS

“Equal Night” and “The Goddess of Beauty & Love”  

This month on the 22nd at 7:21 AM, Earth’s Northern Hemisphere heralds the return of the Fall Season. In astronomical terms this is known as the Autumnal Equinox, “Autumnal” or autumn, and “Equinox”, Latin for “equal night”. On this day, the sun will rise and set due east and due west respectively, and therefore both hemispheres will receive equal amounts of night and day – although in the southern hemisphere, this same event marks the return of Spring. From our perspective here on Earth, we can document this annual event for ourselves. If you were to notice where the sun rises and sets each day over the course of a year, you may notice that the sun moves continuously from north to south and back again. In the summer months, the sun rises and sets further north while in the winter months, the sun rises and sets further south – both reaching their northern and southern extremes on their respective solstices. Solstice is Latin for “stand still”, as the sun appears to slow down and “stand still” before changing directions.  

Since Earth’s axis is always tilted in the same direction, as we orbit the sun there are times of the year when Earth’s top half is leaning towards the sun (Summer – longer days, shorter nights) and times of the year when it’s leaning away from the sun (Winter – shorter days, longer nights). As this transition happens, there are also times when Earth isn’t leaning towards the sun at all, and these are known as the Equinoxes – both Vernal (Spring) and Autumnal (Fall). So, on Thursday, September 22nd, we welcome the return of autumn to the northern, or top half of planet Earth, while our “down under” Australian friends welcome Spring.

Speaking of planets, Venus (named for the Goddess of Beauty and Love) makes her return to our western skies just after sunset. However, she will hug the western horizon until early November, after which she begins a gradual yet steady climb, reaching her summit in early February – then beginning her slow descent, inching towards the glare of the sun and disappearing completely from our western skies by late March.

Mars, named for the Roman God of War and Saturn, named for the Roman God of Agriculture, are still dazzling in the southwest at sunset, but only for a short amount of time. Mars is the bright, steady, pinkish star-like object located approximately halfway up the sky in the south west at sunset. To the right of Mars – almost directly across in a straight line – is the much fainter Saturn. Even though Saturn is HUGE (you could easily fit 9 Earth’s across the widest part of it’s disc), it’s so far away that from Earth (884 million miles / approx. 80 light minutes), it only resembles a fairly bright star. The distance between the two will continue to grow until eventually Saturn, like Venus, slips closer towards the sun’s glare.

But look for Earth’s own natural satellite, The Moon, to approach and slip past both Saturn and Mars! On the evening of September 7th, the waxing crescent moon will approach Saturn, appearing to the right of the ringed giant. The following evening, September 8th, the almost first quarter moon will appear directly above Saturn, and on the next evening, September 9th, the quarter (or half) moon slips even further east and appears slightly higher above the planet Mars.

Enjoy the return of Autumn and remember, “Keep Looking Up!”